With the growing development and widespread proliferation of electricity rich vehicles, such as a hybrid vehicle, an electric vehicle, or a fuel cell vehicle, power supply circuits mounted on such vehicles are increasing in complexity and size. For example, the hybrid vehicle is configured to include a traveling battery, a system battery, an external power supply circuit for plug-in use, a DC/DC converter for supplying a traveling motor with direct current (DC) power from the traveling battery, a DC/AC converter for converting the DC power from the traveling battery into alternating current (AC) power, a DC/DC converter for supplying an electric power steering (EPS) with the DC power from the traveling battery, a DC/DC converter for supplying accessory equipment with the DC power from the travelling battery, etc. This causes the hybrid vehicle including these components to have a complicated circuit configuration.
Under the circumstances, multi-port power supplies having multiple inputs and outputs arranged in one circuit are being developed. It has been suggested that wiring, semiconductor devices, and the like are shared by means of the multi-port power supplies, to thereby downsize power supply circuitry.
JP 2011-193713 A discloses a power conversion circuit having four ports, in which electric power can be converted between arbitrary ports selected from among the four ports.
In such a power conversion circuit having multiple ports, there is a possibility that a circulating current that does not function to transmit electric power may be created by error components resulting from dead time, voltage variations, or other factors. In the conventional art, however, no attention has been paid to the circulating current, resulting in a problem that conversion efficiency is reduced by the presence of the circulating current. As used herein, the circulating current denotes a current that should, under ideal conditions, become zero when a closed circuit is created by turning on the two upper or the two lower switches among the four switches constituting a full bridge, yet could flow through the closed circuit due to an inductance component in a coupling reactor, a resistance component in each part, or other components.